What to use on badly worn AF 4-8-4 Northern sideframe axle bearing holes?

Thanks BanjoFlyer, but PA 10240 is the insulating bushing used to insulate the truck from the metal chassis.  It is used in conjunction with rivet PA9988 and washer PA8715-B.  It is not used in side frames.  

If you look at the later tender truck side frames, you will see that they do not protrude downward below the axles and the simulated axle bearings as far as the earlier ones do. I ground mine off with a Dremel to match the later side frame design.

Perhaps you should inquire with Ed of Goldinhands Train Repair. He advertises bushing upgrades to AF chassis and rolling stock trucks. Perhaps he is familiar with the same for tender trucks.

RoyBoy, interesting.  By later production do you mean later AC Gilbert production or Lionel AF?  Can you provide photos to see the comparison?  Thanks.

The Hudson and Northerns use the same trucks and both show up with the problem described. For engines that are used infrequently, like running on a holiday layout there is a very simple fix. Remove the wheel sets from the tender trucks, bend down the brass axle wipers to increase the pressure and reinstall the wheel sets. I have two engines with worn tender axle holes I repaired this way over 5 years ago and they still run fine on the Christmas layout. 

I also repaired one as an experiment by applying some liquid electrical tape on the bottom of the tender truck side frame. It worked but I am not sure how long it will last. The 660 series extruded aluminum passenger car trucks can also have the same wear followed by shorting problem. I tried repairing one by filling in the worn part of the hole with the metallic infused epoxy. It worked but was a real pain to do. I will not use that method again.

There are bushings made for this repair and Goldinhands offers that repair service. As sgaugian pointed out the axles do need to have some freedom of up and down movement for the trucks to track properly. Grinding off the offending metal on the underside of the side frame also works. I have found bending the brass axle wipers the simplest and adequate for the amount of operating time I put on any individual engine. 

Adding extra axle wiper pressure on the axles to actually lift the tender, passenger car, etc. higher off the rails is one approach.  However, the trade off is that with some heavy tenders and/or cars the added pressure required can add roll resistance (making it harder for the engine to pull that tender, etc.) and faster wear of the wiper and/or axles involved.  I'm looking for something that allows normal wiper pressure (i.e. keeps it as easy rolling as possible), but lifts the bottom edges of the side frames higher off the rails.  I think the grinding of those edges is the most practical approach at this time.  

PS On one 321 Hudson with worn axle bearing holes, I installed brass KC car truck eyelets into the outside axle holes, but not the middle axle holes. I then attached a steamer pilot conical coil spring under the middle axle that makes contact with that axle and the truck's frame. Early Hudsons came with three axle sets.  That way the side frames were lifted back to their correct height off the rails, the axle wipers have normal pressure on the outside axles, and the middle axle can float while maintaining contact with the rails and truck frame even if the tender lifts or tilts a bit.  It works so far on my layout and our club layouts, but that conical spring on the middle axle is key.  

Sgaugian posted:

RoyBoy, interesting.  By later production do you mean later AC Gilbert production or Lionel AF?  Can you provide photos to see the comparison?  Thanks.

I do not have a camera, but here is what I have observed. Look at the round circle on the outside side frame that simulates the axle bearing - three on each side. The early side frames have a rectangular protrusion, simulating the bearing slide,  that sticks down a 1/16" or so below the circle/bearing. The later side frames end at the circle/bearing - they do not stick down below the circle/bearing and are flush with the bottom of the circle.

My thinking is that the change happened with/around the change from link couplers to knuckle couplers - all in the Gilbert era.

RoyBoy -- excellent point and observation.  My 321 LC era Hudson has those extensions that go below the bearing caps (i.e. closer to the track).  My 336 KC era Northern side frames do not.